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.\"     @(#)getitimer.2	8.3 (Berkeley) 5/16/95
.\"
.Dd October 27, 2011
.Dt GETITIMER 2
.Os
.Sh NAME
.Nm getitimer ,
.Nm setitimer
.Nd get/set value of interval timer
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/time.h
.Ft int
.Fn getitimer "int which" "struct itimerval *value"
.Ft int
.Fn setitimer "int which" "const struct itimerval * restrict value" "struct itimerval * restrict ovalue"
.Sh DESCRIPTION
The system provides each process with three interval timers,
defined in
.Ao Pa sys/time.h Ac .
The
.Fn getitimer
call returns the current value for the timer specified in
.Fa which
in the structure at
.Fa value .
The
.Fn setitimer
call sets a timer to the specified
.Fa value ,
returning the previous value of the timer if
.Fa ovalue
is not
.Dv NULL .
.Pp
A timer value is defined by the
.Fa itimerval
structure:
.Bd -literal -offset indent
struct itimerval {
	struct	timeval it_interval;	/* timer interval */
	struct	timeval it_value;	/* current value */
};
.Ed
.Pp
If
.Fa it_value
is non-zero, it indicates the time to the next timer expiration.
If
.Fa it_interval
is non-zero, it specifies a value to be used in reloading
.Fa it_value
when the timer expires.
Setting
.Fa it_value
to 0 disables a timer.
Setting
.Fa it_interval
to 0 causes a timer to be disabled after its next expiration (assuming
.Fa it_value
is non-zero).
.Pp
The
.Fa which
parameter specifies the type of the timer:
.Bl -tag -width "ITIMER_MONOTONIC " -offset indent
.It Dv ITIMER_REAL
timer decrements in real time.
This timer is affected by
.Xr adjtime 2
and
.Xr settimeofday 2 .
A
.Dv SIGALRM
signal is
delivered when this timer expires.
.It Dv ITIMER_VIRTUAL
timer decrements in process virtual time.
It runs only when the process is executing.
A
.Dv SIGVTALRM
signal
is delivered when it expires.
.It Dv ITIMER_PROF
timer decrements both in process virtual time and
when the system is running on behalf of the process.
It is designed to be used by interpreters in statistically profiling
the execution of interpreted programs.
Each time the
.Dv ITIMER_PROF
timer expires, the
.Dv SIGPROF
signal is
delivered.
Because this signal may interrupt in-progress
system calls, programs using this timer must be prepared to
restart interrupted system calls.
.It Dv ITIMER_MONOTONIC
timer decrements in monotonic time.
This timer is not affected by
.Xr adjtime 2
and
.Xr settimeofday 2 .
A
.Dv SIGALRM
signal is
delivered when this timer expires.
.El
Note that:
.Bl -bullet -offset indent
.It
Time values smaller than the resolution of the
system clock are rounded up to this resolution
(typically 10 milliseconds).
.It
The interaction between
.Fn setitimer
and
.Xr alarm 3
or
.Xr sleep 3
is unspecified by the specification.
.El
.Sh RETURN VALUES
If the calls succeed, a value of 0 is returned.
If an error occurs, the value \-1 is returned, and a more precise error
code is placed in the global variable
.Va errno .
.Sh ERRORS
Both functions may fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
The
.Fa value
parameter specified a bad address.
.It Bq Er EINVAL
The
.Fa which
parameter was not a known timer type, or the
.Fa value
parameter specified a time that was too large
to be handled.
.El
.Sh SEE ALSO
.Xr gettimeofday 2 ,
.Xr select 2 ,
.Xr sigaction 2 ,
.Xr itimerval 3 ,
.Xr timeradd 3
.Sh STANDARDS
The functions conform to
.St -p1003.1-2001 .
The later
.St -p1003.1-2008
revision however marked both as obsolescent,
recommending the use of
.Xr timer_gettime 2
and
.Xr timer_settime 2
instead.
.Sh HISTORY
The
.Fn getitimer
function call appeared in
.Bx 4.2 .
The
.Dv ITIMER_MONOTONIC
functionality appeared in
.Nx 6.0 .
